<html>
  <head>
    <title>flex学习</title>
    <meta charset="utf8" />
    <style>
      body {
        margin: 0;
        background-color: beige;
        height: 100%;
      }
      .upper {
        
        background-color:coral;
        display: flex;
        height: 200px;
        flex-wrap: nowrap;
        /* flex-direction主轴的方向 */
        flex-direction: column;
        /* justify-content主轴上对其方式 */
        justify-content: space-around;
        /* align-items交叉轴对齐方式 */
        align-items: flex-end;      

      }
      .first {
        background-color: aqua;
        width: 300px;
        margin-right: 10px;
      }
      .second {
        background-color: aquamarine;
        width: 400px;
        margin-right: 20px;

      }
      .third {
        background-color: blueviolet;
      }
      .fourth {
        background-color: brown;
      }
    </style>
  </head>
  <body>
    <div class="upper">
      <div class="first">第一个</div>
      <div class="second">第二个</div>
      <div class="third">第三个</div>
      <div class="fourth">第四个</div>
    </div>
  </body>
</html>